gas laws and heat engine - physlab › ... › gaslawsandheatenginev1.pdfwaqas mahmood and muhammad...
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W A Q A S M A H M O O D A N D M U H A M M A D S A B I E H A N W A R
L U M S , S C H O O L O F S C I E N C E & E N G I N E E R I N G( 2 9 A P R I L , 2 0 1 1 )
Gas Laws and the Heat Engine
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Outline
Introduction Calibration of potentiometer Charles’s law Pressure versus temperature Boyle’s law Making a heat engine Results Conclusion
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Introduction
This work has been described in,
David P. Jackson and Priscilla W. Laws, Syringethermodynamics: The many uses of a glass syringe,American Journal of Physics, (2005).
We will be using a linear potentiometer to measurethe change in volume in our experiment. Thisexperiment has been finally included in the freshmenlab.
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Placing the thermocouple inside the flask
• Place the thermocouple inside the flask.• Seal it properly using Teflon tape or silicone available in our workshop.• Connect the thermocouple to multi-meter with a selection to measure temperature.
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Selection of flask
We have flasks of different volumes but the choice is important to have reasonable expansion of the syringe.
We have used a pipette to measurethe volume of the flask (since, thegas occupies the volume of thecontainer).
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Pressure sensor
MPXH6400 (Manufacturer: free scale semiconductors), the date sheet can be downloaded from http://www.freescale.com/.
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Calibration of the Potentiometer
Calibration equation is, Y = 0.002 X – 7.9 e - 5
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Charles’s Law :Volume vs Temperature
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Absoulte zero of temperature
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Pressure versus Temperature
Make sure you do not exceed the bearing pressure of flask.
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Data with a curve fit
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Boyle’s Law: Pressure versus Volume
Either pull or push the plunger.
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Data obtained: V = Constant/P
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Making a heat engine
Salman Mahmood Qazi (A student of Electronics atthe Government College University) worked on themaking of a potentiometer.
Imran Hanif worked on the electronic data takingbut he was unable to get a complete cycle.
Waqas Mahmood started working on theexperimental data taking after Imran.
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• Initially balance the potentiometer for the free movement of the sliding contact.• Friction may give not required but interesting results.
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Results: Trial 39
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Trial 52
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Calculation for the area under the curve
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Calculation for Efficiencies
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Gamma for air using PV = constant
We have obtained the value of Ґ ~ 1.0 that is in close to the published value of 1.3 by PaulF. Rebillot, Determining the Ratio Cp/Cv using Rucchart's Method, Wooster, Ohio, April(1998), http://www3.wooster.edu/physics/jris/Files/Rebillot.pdf.
ґ
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Conclusion
We have achieved a mechanical efficiency > 70% and thermodynamic efficiency of < 1%.
Can we improve it and how much?
Yes! We can improve slightly but not much. If we have flasks up to 25 mL volume, the PV curve might be in a more
desired shape. Even if you go to more smaller volumes, we can not increase the
thermodynamic efficiency > 1%. Reason: If the volume of the container is made much smaller than
25mL, the air inside the flask may not be able to lift the piston.
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Although, this setup does not yield better thermodynamic efficiency butit teaches basic concepts such as pressure, heat, work done and internalenergy etc. powerfully.
It serves as a small bridge between theoretical understanding ofthermodynamics and experimental application at the freshmen level.
Thanks